Microsoft has finally made available its long awaited update to Skype for the Windows Phone 8 operating system, but it's still only in preview.

The popular VoIP program, which allows voice and video messaging across the Internet for free, is available to download on the Windows Phone app store.

On the Skype blog, Microsoft says that the "experiences are not yet final" with the preview version of the app, and lists many issues which the company is working to resolve.

These include only the front camera being supported for video calling at the moment, missed calls not appearing on the phone's home screen live tile, no support for sending SMS texts with the app, and lack of support for Bluetooth headsets.

What is available, however, are "all of the Skype basics in the new, modern design along with many of the new features such as integration with the People Hub and a combined contact list with buddies from Windows Live Messenger," said Microsoft. "Additionally, you'll start receiving some call and message notifications - even when the app is closed and in the background."

Microsoft bought Skype last year for $8.5 billion and last week said it will become its default messaging program ahead of its popular Windows Live Messenger.

Messenger is due for retirement in the first quarter of 2013, except in China, and, as part of this plan, Microsoft is automatically integrating Messenger buddies into Skype.

Skype will be one of the big features of Microsoft's recently released Windows Phone 8 OS, which can already be found on the Nokia Lumia 920 and HTC 8X smartphones.

Once installed, the 8MB download integrates itself with the People Hub on your phone, allowing you to choose to make a Skype call, standard call, send a text, email or Facebook message.

Those running the older Windows Phone 7 on the Lumia 800, already have a previous version of Skype, which can also be downloaded for Android and iOS.

Microsoft says, "The new Skype for Windows Phone will be fast, modern, and beautiful, while still delivering the best of what you've come to expect from Skype."

The preview can be downloaded from windowsphone.com.